Dense Wavelength Division Multiplexing (DWDM), and Coarse Wavelength Division Multiplexing (CWDM) are techniques for increasing the bandwidth of optical network communications. CWDM allows for eighteen different data signals to be transmitted simultaneously over a pair of fibers. DWDM allows many (e.g., dozens) of different data signals to be transmitted simultaneously over a pair of fibers. To keep the signals distinct, CWDM/DWDM manipulates wavelengths of light to keep each signal within its own narrow band. Depending upon the application, CWDM/DWDM is a generally more cost-effective alternative to Time Division Multiplexing (TDM).
CWDM and DWDM Pluggable Transceivers are typically provided at relatively higher cost, and longer lead time product. This is due to the nature of the product itself: typical CWDM hot-swappable, pluggable transceivers are offered in a total of 18 different standardized channels used for various applications. Similarly, ‘fixed channel’ DWDM hot-swappable, pluggable transceivers are offered in no less than 40 different channels (e.g., as specified by the 100 GHz channel spacing standardized by the ITU), and different organizations and different switch and router manufacturers have a variety of needs for groups of these channels. Because of the continued need for higher bandwidth connectivity for the generalized ‘service provider’ market, coupled with a general scarcity of fiber availability (or the need for conservation of fiber plant due to new mandates by the construction arms of these providers), the market finds itself in a position where multiplexing solutions (CWDM and DWDM) are an attractive methodology for maximizing the fiber infrastructure with minimal operational impact, requiring only incremental capital expenditure.
The situation—as it stands today—is summarized as follows: different end users have different channel requirements, planning schema, and rollout procedures that do not synchronize with the typical lead times for these pluggable optics. That lead time is typically 8 to 12 weeks, if not longer. This lead time can often push out revenue for the end user (service provider) or cause loss of contractual business due to inability to bring up services in a timely—or more competitive—manner.
Tunable transceivers have existed in systems for some time. However, they were proprietary, card- or blade-based solutions that were NOT hot-swappable or hot-pluggable, were not industry standard (each vendor had their own mechanism for tuning of the channel via their own software) and were not cost effective.
The advent of the pluggable version of a tunable DWDM transceiver, in the standard XFP form factor, meant that the proprietary aspects of the blade-based solutions were removed. The benefits of an MSA-compliant pluggable optical transceiver would mean that electrical, optical, and mechanical specifications would be standardized, and that any manufacturers of switches or routers that utilize these form factors for their 10 GBase (10 Gigabit Ethernet), 10G Fibre Channel, or SONET OC-192 ports would now have access to a tunable solution.
However, these platforms would need modified operating system software which would have the capacity to access the EEPROM of the XFP transceiver via the I2C communication bus and set the channel or wavelength (these terms are used interchangeably, though they are not synonymous in the most literal sense). The platforms that have this capability are typically higher-end, higher density core or access devices, and therefore the ‘edge’ or ‘customer premise’ level-devices are still left without a solution.